Re: [PATCH v3] integrity: support including firmware ".platform" keys at build time

[Nayna <nayna@xxxxxxxxxxxxxxxxxx>]

On 11/5/21 10:05, Dimitri John Ledkov wrote:
> (Changing Seth's email to personal domain one)
>
> On 04/10/2021 15:52, Nayna Jain wrote:
> > Some firmware support secure boot by embedding static keys to verify the
> > Linux kernel during boot. However, these firmware do not expose an
> > interface for the kernel to load firmware keys onto ".platform" keyring.
> > This would prevent kernel signature verification on kexec.
> >
> > For these environments, a new function load_builtin_platform_cert() is
> > defined to load compiled in certificates onto the ".platform" keyring.
> >
> > load_certificate_list() is currently used for parsing compiled in
> > certificates to be loaded onto the .builtin or .blacklist keyrings.
> > Export load_certificate_list() allowing it to be used for parsing compiled
> > in ".platform" keyring certificates as well.
> >
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>(auto build test ERROR)
> > Signed-off-by: Nayna Jain <nayna@xxxxxxxxxxxxx>
> > ---
> > NOTE: I am wondering if we should split this patch into two:
> > (https://lore.kernel.org/linux-integrity/be4bd13d-659d-710d-08b9-1a34a65e5c5d@xxxxxxxxxxxxxxxxxx/).
> > I can do so if you also prefer the same.
> Yes, i think you should split the patches into refactor & new feature.
> It allows one to clearly inspect/validate the no-change refactor, and
> separately review the newly added feature with clarity.
>
> Or maybe avoid the refactor all together, see my optional suggestion at
> the end.

Thanks Dimitri for the feedback. Sorry for the delay in the response, I 
was on vacation last week.  Yes, I have split the patches now for next 
version. Answers to other comments are inline.


> > v3:
> > * Included Jarkko's feedback
> >   ** updated patch description to include approach.
> >   ** removed extern for function declaration in the .h file.
> > * Included load_certificate_list() within #ifdef CONFIG_KEYS condition.
> >
> > v2:
> > * Fixed the error reported by kernel test robot
> > * Updated patch description based on Jarkko's feedback.
> >
> >   certs/Makefile                                |  3 ++-
> >   certs/blacklist.c                             |  1 -
> >   certs/common.c                                |  2 +-
> >   certs/common.h                                |  9 -------
> >   certs/system_keyring.c                        |  1 -
> >   include/keys/system_keyring.h                 |  6 +++++
> >   security/integrity/Kconfig                    | 10 +++++++
> >   security/integrity/Makefile                   | 17 +++++++++++-
> >   security/integrity/digsig.c                   |  2 +-
> >   security/integrity/integrity.h                |  6 +++++
> >   .../integrity/platform_certs/platform_cert.S  | 23 ++++++++++++++++
> >   .../platform_certs/platform_keyring.c         | 26 +++++++++++++++++++
> >   12 files changed, 91 insertions(+), 15 deletions(-)
> >   delete mode 100644 certs/common.h
> >   create mode 100644 security/integrity/platform_certs/platform_cert.S
> >
> > diff --git a/certs/Makefile b/certs/Makefile
> > index 279433783b10..64ee37f38b85 100644
> > --- a/certs/Makefile
> > +++ b/certs/Makefile
> > @@ -3,7 +3,8 @@
> >   # Makefile for the linux kernel signature checking certificates.
> >   #
> >   
> > -obj-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += system_keyring.o system_certificates.o common.o
> > +obj-$(CONFIG_KEYS) += common.o
> > +obj-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += system_keyring.o system_certificates.o
> >   obj-$(CONFIG_SYSTEM_BLACKLIST_KEYRING) += blacklist.o common.o
> >   obj-$(CONFIG_SYSTEM_REVOCATION_LIST) += revocation_certificates.o
> >   ifneq ($(CONFIG_SYSTEM_BLACKLIST_HASH_LIST),"")
> > diff --git a/certs/blacklist.c b/certs/blacklist.c
> > index c9a435b15af4..b95e9b19c42f 100644
> > --- a/certs/blacklist.c
> > +++ b/certs/blacklist.c
> > @@ -17,7 +17,6 @@
> >   #include <linux/uidgid.h>
> >   #include <keys/system_keyring.h>
> >   #include "blacklist.h"
> > -#include "common.h"
> >   
> >   static struct key *blacklist_keyring;
> >   
> > diff --git a/certs/common.c b/certs/common.c
> > index 16a220887a53..41f763415a00 100644
> > --- a/certs/common.c
> > +++ b/certs/common.c
> > @@ -2,7 +2,7 @@
> >   
> >   #include <linux/kernel.h>
> >   #include <linux/key.h>
> > -#include "common.h"
> > +#include <keys/system_keyring.h>
> >   
> >   int load_certificate_list(const u8 cert_list[],
> >   			  const unsigned long list_size,
> > diff --git a/certs/common.h b/certs/common.h
> > deleted file mode 100644
> > index abdb5795936b..000000000000
> > --- a/certs/common.h
> > +++ /dev/null
> > @@ -1,9 +0,0 @@
> > -/* SPDX-License-Identifier: GPL-2.0-or-later */
> > -
> > -#ifndef _CERT_COMMON_H
> > -#define _CERT_COMMON_H
> > -
> > -int load_certificate_list(const u8 cert_list[], const unsigned long list_size,
> > -			  const struct key *keyring);
> > -
> > -#endif
> > diff --git a/certs/system_keyring.c b/certs/system_keyring.c
> > index 692365dee2bd..d130d5a96e09 100644
> > --- a/certs/system_keyring.c
> > +++ b/certs/system_keyring.c
> > @@ -16,7 +16,6 @@
> >   #include <keys/asymmetric-type.h>
> >   #include <keys/system_keyring.h>
> >   #include <crypto/pkcs7.h>
> > -#include "common.h"
> >   
> >   static struct key *builtin_trusted_keys;
> >   #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
> > diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
> > index 6acd3cf13a18..d3f914d9a632 100644
> > --- a/include/keys/system_keyring.h
> > +++ b/include/keys/system_keyring.h
> > @@ -10,6 +10,12 @@
> >   
> >   #include <linux/key.h>
> >   
> > +#ifdef CONFIG_KEYS
> > +int load_certificate_list(const u8 cert_list[],
> > +			  const unsigned long list_size,
> > +			  const struct key *keyring);
> > +#endif
> > +
> >   #ifdef CONFIG_SYSTEM_TRUSTED_KEYRING
> >   
> >   extern int restrict_link_by_builtin_trusted(struct key *keyring,
> > diff --git a/security/integrity/Kconfig b/security/integrity/Kconfig
> > index 71f0177e8716..b2009b792882 100644
> > --- a/security/integrity/Kconfig
> > +++ b/security/integrity/Kconfig
> > @@ -62,6 +62,16 @@ config INTEGRITY_PLATFORM_KEYRING
> >            provided by the platform for verifying the kexec'ed kerned image
> >            and, possibly, the initramfs signature.
> >   
> > +config INTEGRITY_PLATFORM_BUILTIN_KEYS
> > +        string "Builtin X.509 keys for .platform keyring"
> > +        depends on KEYS
> > +        depends on ASYMMETRIC_KEY_TYPE
> > +        depends on INTEGRITY_PLATFORM_KEYRING
> > +        help
> > +          If set, this option should be the filename of a PEM-formatted file
> > +          containing X.509 certificates to be loaded onto the ".platform"
> > +          keyring.
> > +
> >   config LOAD_UEFI_KEYS
> >          depends on INTEGRITY_PLATFORM_KEYRING
> >          depends on EFI
> > diff --git a/security/integrity/Makefile b/security/integrity/Makefile
> > index 7ee39d66cf16..a45f083589b8 100644
> > --- a/security/integrity/Makefile
> > +++ b/security/integrity/Makefile
> > @@ -3,13 +3,18 @@
> >   # Makefile for caching inode integrity data (iint)
> >   #
> >   
> > +quiet_cmd_extract_certs  = EXTRACT_CERTS   $(patsubst "%",%,$(2))
> > +      cmd_extract_certs  = scripts/extract-cert $(2) $@
> > +$(eval $(call config_filename,INTEGRITY_PLATFORM_BUILTIN_KEYS))
> > +
> >   obj-$(CONFIG_INTEGRITY) += integrity.o
> >   
> >   integrity-y := iint.o
> >   integrity-$(CONFIG_INTEGRITY_AUDIT) += integrity_audit.o
> >   integrity-$(CONFIG_INTEGRITY_SIGNATURE) += digsig.o
> >   integrity-$(CONFIG_INTEGRITY_ASYMMETRIC_KEYS) += digsig_asymmetric.o
> > -integrity-$(CONFIG_INTEGRITY_PLATFORM_KEYRING) += platform_certs/platform_keyring.o
> > +integrity-$(CONFIG_INTEGRITY_PLATFORM_KEYRING) += platform_certs/platform_keyring.o \
> > +						  platform_certs/platform_cert.o
> >   integrity-$(CONFIG_LOAD_UEFI_KEYS) += platform_certs/efi_parser.o \
> >   				      platform_certs/load_uefi.o \
> >   				      platform_certs/keyring_handler.o
> > @@ -19,3 +24,13 @@ integrity-$(CONFIG_LOAD_PPC_KEYS) += platform_certs/efi_parser.o \
> >                                        platform_certs/keyring_handler.o
> >   obj-$(CONFIG_IMA)			+= ima/
> >   obj-$(CONFIG_EVM)			+= evm/
> > +
> > +
> > +$(obj)/platform_certs/platform_cert.o: $(obj)/platform_certs/platform_certificate_list
> > +
> > +targets += platform_certificate_list
> > +
> > +$(obj)/platform_certs/platform_certificate_list: scripts/extract-cert $(INTEGRITY_PLATFORM_BUILTIN_KEYS_FILENAME) FORCE
> > +	$(call if_changed,extract_certs,$(CONFIG_INTEGRITY_PLATFORM_BUILTIN_KEYS))
> > +
> > +clean-files := platform_certs/platform_certificate_list
> > diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
> > index 3b06a01bd0fd..0ea40ed8dfcb 100644
> > --- a/security/integrity/digsig.c
> > +++ b/security/integrity/digsig.c
> > @@ -38,7 +38,7 @@ static const char * const keyring_name[INTEGRITY_KEYRING_MAX] = {
> >   #define restrict_link_to_ima restrict_link_by_builtin_trusted
> >   #endif
> >   
> > -static struct key *integrity_keyring_from_id(const unsigned int id)
> > +struct key *integrity_keyring_from_id(const unsigned int id)
> >   {
> >   	if (id >= INTEGRITY_KEYRING_MAX)
> >   		return ERR_PTR(-EINVAL);
> > diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h
> > index 547425c20e11..feb84e1b1105 100644
> > --- a/security/integrity/integrity.h
> > +++ b/security/integrity/integrity.h
> > @@ -167,6 +167,7 @@ int __init integrity_init_keyring(const unsigned int id);
> >   int __init integrity_load_x509(const unsigned int id, const char *path);
> >   int __init integrity_load_cert(const unsigned int id, const char *source,
> >   			       const void *data, size_t len, key_perm_t perm);
> > +struct key *integrity_keyring_from_id(const unsigned int id);
> >   #else
> >   
> >   static inline int integrity_digsig_verify(const unsigned int id,
> > @@ -194,6 +195,11 @@ static inline int __init integrity_load_cert(const unsigned int id,
> >   {
> >   	return 0;
> >   }
> > +
> > +static inline struct key *integrity_keyring_from_id(const unsigned int id)
> > +{
> > +	return ERR_PTR(-EOPNOTSUPP);
> > +}
> >   #endif /* CONFIG_INTEGRITY_SIGNATURE */
> >   
> >   #ifdef CONFIG_INTEGRITY_ASYMMETRIC_KEYS
> > diff --git a/security/integrity/platform_certs/platform_cert.S b/security/integrity/platform_certs/platform_cert.S
> > new file mode 100644
> > index 000000000000..20bccce5dc5a
> > --- /dev/null
> > +++ b/security/integrity/platform_certs/platform_cert.S
> > @@ -0,0 +1,23 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> My personal preference would be to have platform_cert.S next to all the
> other "extract certs and build an object out of them", as in
> /certs/platform_cert.S right next to the other similar .S files, i.e
> system_certificates.S and revocation_certificates.S it would make it
> easier to inspect the build and find all the various types of built-in keys.
>
> This is a minor comment/suggestion, that you can reject.

I think anything platform related should be in the platform_certs/ 
directory.


> > +#include <linux/export.h>
> > +#include <linux/init.h>
> > +
> > +	__INITRODATA
> > +
> > +	.align 8
> > +#ifdef CONFIG_INTEGRITY_PLATFORM_KEYRING
> > +	.globl platform_certificate_list
> > +platform_certificate_list:
> > +__cert_list_start:
> > +	.incbin "security/integrity/platform_certs/platform_certificate_list"
> > +__cert_list_end:
> > +#endif
> > +
> > +	.align 8
> > +	.globl platform_certificate_list_size
> > +platform_certificate_list_size:
> > +#ifdef CONFIG_64BIT
> > +	.quad __cert_list_end - __cert_list_start
> > +#else
> > +	.long __cert_list_end - __cert_list_start
> > +#endif
> > diff --git a/security/integrity/platform_certs/platform_keyring.c b/security/integrity/platform_certs/platform_keyring.c
> > index bcafd7387729..17535050d08d 100644
> > --- a/security/integrity/platform_certs/platform_keyring.c
> > +++ b/security/integrity/platform_certs/platform_keyring.c
> > @@ -12,8 +12,12 @@
> >   #include <linux/cred.h>
> >   #include <linux/err.h>
> >   #include <linux/slab.h>
> > +#include <keys/system_keyring.h>
> >   #include "../integrity.h"
> >   
> > +extern __initconst const u8 platform_certificate_list[];
> > +extern __initconst const unsigned long platform_certificate_list_size;
> > +
> >   /**
> >    * add_to_platform_keyring - Add to platform keyring without validation.
> >    * @source: Source of key
> > @@ -37,6 +41,28 @@ void __init add_to_platform_keyring(const char *source, const void *data,
> >   		pr_info("Error adding keys to platform keyring %s\n", source);
> >   }
> >   
> I think the below hunk should be guarded with #ifdef
> CONFIG_INTEGRITY_PLATFORM_BUILTIN_KEYS, similar to how similar call is
> ifdef'ed in case of revocation keys i.e. see ifdef
> CONFIG_SYSTEM_REVOCATION_LIST in certs/blacklist.c. Because one can
> configure a kernel with a platform keyring, but without platform builtin
> keys.
>
> I think this must be be fixed.

If there are no builtin keys configured, then size would be zero and 
load_certificate_list would just return. I am not sure why it had to be 
ifdef'ed for revocation, I do not see the same for loading system 
certificates onto system keyring. Please let me know if you think I am 
missing something.


> > +static __init int load_builtin_platform_cert(void)
> > +{
> > +	const u8 *p;
> > +	unsigned long size;
> > +	int rc;
> > +	struct key *keyring;
> > +
> > +	p = platform_certificate_list;
> > +	size = platform_certificate_list_size;
> > +
> > +	keyring = integrity_keyring_from_id(INTEGRITY_KEYRING_PLATFORM);
> > +	if (IS_ERR(keyring))
> > +		return PTR_ERR(keyring);
> > +
> > +	rc = load_certificate_list(p, size, keyring);
> > +	if (rc)
> > +		pr_info("Error adding keys to platform keyring %d\n", rc);
> > +
> > +	return rc;
> > +}
> > +late_initcall(load_builtin_platform_cert);
> > +
>
> Some more general comment:
> I do wonder if the refactor of load_certificate_list can be somehow
> avoided. For example, when platform keyring is allocated it calls
> set_platform_trusted_keys() from certs/system-keyring.c which could add
> a call to load_builtin_platform_cert, and it already has a handle to the
> platform keyring. The set_platform_trusted_keys() could call to
> load_certificate_list there without late_initcall, alocating variables,
> and looking up the integrity_keyring_from id. It would make this feature
> patch very concise and straight forward then.
>
> That way builtin platform certs will be done before platform specific
> load_*.c things are done. But also it will make builtin certs loading be
> done in a different place from the rest of the platform certs loading
> (e.g. the uefi one). So maybe doing builtin certs loading, next to all
> other platform cert loading makes sense, despite it being away from
> other builtin certs loading into other keyrings.
>
> I am divided on this =)

Yes, I had also thought about it. I saw that set_platform_trusted_keys() 
call is dependent on CONFIG_SYSTEM_TRUSTED_KEYRING. By design, it should 
be possible to load platform certs onto the platform keyring even when 
the system keyring is not enabled. So, I preferred to keep it separate 
and in platform_keyring.c.

Thanks & Regards,

      - Nayna